Characterization of novel LAP1 complexes and their relevance in DYT1 dystonia

• Autor(a) principal: Graça, Mariana Santos Moreda
• Data de Publicação: 2014
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/13282
• topic: Ciências biomédicas; Proteínas - Fosforilação; Interacções proteína-proteína

Dystonia is the third most common movement disorder, following essential tremor and Parkinson’s disease, and comprises a large number of clinical syndromes. DYT1 dystonia is recognized as the most common form of early onset isolated dystonia and is caused by a mutation in the DYT1 gene, resulting in the loss of a single glutamic acid within the torsinA protein (ΔE-torsinA). TorsinA resides in the endoplasmic reticulum and nuclear envelope (NE), but the mutant form is abnormally relocated to the NE. At the NE, torsinA interacts with lamina associated polypeptide 1 (LAP1), whose function is poorly understood. LAP1 is a transmembrane protein of the inner nuclear membrane that was described to exist as three alternatively spliced isoforms (LAP1A, B and C) in rat. Protein-protein interactions are becoming increasingly important in the study of human diseases and signaling pathways. In this work, human LAP1B was identified as a novel protein phosphatase 1 (PP1) binding protein. PP1 is a major Ser/Thr phosphatase that is estimated to dephosphorylate about one third of all proteins in eukaryotic cells. The versatility of PP1 is only possible by complexing with different binding proteins that play regulatory and targeting roles. We found that LAP1B is a substrate of PP1 and binds to the latter through an RVxF-like motif located in the nucleoplasmic domain. In the course of this work, we also identified a novel human LAP1 isoform - LAP1C that is N-terminally truncated. Human LAP1B and LAP1C isoforms seem to be developmentally regulated and are both dephosphorylated by PP1. Moreover, LAP1 proteins seem to be important for NE integrity and mitosis regulation. Given that PP1 interacts with LAP1 in the nucleoplasm, which in turn interacts with torsinA in the perinuclear space, the existence of the tricomplex PP1/LAP1/torsinA was validated in rat brain and cultured cells. Moreover, torsinA was dephosphorylated by PP1 but probably binds to the latter via LAP1. The aberrant behavior of ΔE-torsinA in the NE implicates nuclear dysfunction in DYT1 dystonia pathogenesis. Thereby, the role of LAP1 complexes in the NE and its regulation by protein phosphorylation may underlie the pathology of DYT1 dystonia and other NE-related diseases. Moreover, DYT1 dystonia has been related with a dysfunction in the basal ganglia circuit, including dopamine signaling disturbance. Interestingly, PP1/DARPP-32 cascade plays a key role in mediating the actions of dopamine and modulating the phosphorylation and activity of effectors in dopaminoceptors neurons. Thus, our results may lead to novel insights into the molecular and cellular mechanisms of DYT1 dystonia, where protein phosphorylation cascades represent a regulatory mechanism.